This invention relates to a valve for a fluid pressure motor. The valve responds to an operator input to control the communication of fluid through a hub from a first source to both sides of a diaphragm that separates a housing into first and second chambers in a first mode of operation and from a second source to the second chamber to create a pressure differential across the diaphragm in a second mode of operation. This pressure differential acts on the diaphragm and produces an output force which corresponds to an input force.
Control valves in the prior art of which the poppet valve disclosed in U.S. Pat. No. 3,053,235 and the slide valve disclosed in U.S. Pat. No. 3,106,873 are typical, are adequate for most operational needs. However, with a decrease in the size of vehicles, the under hood available space for fluid pressure motors has also decreased making it desirable to make such fluid pressure motors more compact without reducing the efficiency thereof.
In fluid pressure motors having poppet valves, the overall axial dimension from the sealing face to the rear of the attachment bead on the hub of the movable wall is between 3/4" to 1". However, the actual movement required by the sealing face to control the communication of fluid between passages in the hub and the bore is only about 1/8". If the overall axial length of the poppet valve were reduced to approximately the operational travel length, the axial dimension of the hub of the fluid pressure motor could correspondingly be reduced and as such could be easier located in available under hood space of the vehicle.
Similarly in fluid pressure motors having slide valves, the operational travel is dependent on the size of the passage in the hub and the width of the sealing rib. Unfortunately in such slide valves, wear or scoring can damage the sealing surfaces and as a result after a period of use the operational pressure differential is reduced since leak paths develop between the various passages. Thus, such slide valves have not received customer acceptance for use in fluid pressure motors of brake systems of vehicles.